Detailed Description

Note: Default values are not defined for members of MQTTClient_connectOptions so it is good practice to specify all settings. If the MQTTClient_connectOptions structure is defined as an automatic variable, all members are set to random values and thus must be set by the client application. If the MQTTClient_connectOptions structure is defined as a static variable, initialization (in compliant compilers) sets all values to 0 (NULL for pointers). A keepAliveInterval setting of 0 prevents correct operation of the client and so you must at least set a value for keepAliveInterval.

The "keep alive" interval, measured in seconds, defines the maximum time that should pass without communication between the client and the server The client will ensure that at least one message travels across the network within each keep alive period. In the absence of a data-related message during the time period, the client sends a very small MQTT "ping" message, which the server will acknowledge. The keep alive interval enables the client to detect when the server is no longer available without having to wait for the long TCP/IP timeout.

This is a boolean value. The cleansession setting controls the behaviour of both the client and the server at connection and disconnection time. The client and server both maintain session state information. This information is used to ensure "at least once" and "exactly once" delivery, and "exactly once" receipt of messages. Session state also includes subscriptions created by an MQTT client. You can choose to maintain or discard state information between sessions.

When cleansession is true, the state information is discarded at connect and disconnect. Setting cleansession to false keeps the state information. When you connect an MQTT client application with MQTTClient_connect(), the client identifies the connection using the client identifier and the address of the server. The server checks whether session information for this client has been saved from a previous connection to the server. If a previous session still exists, and cleansession=true, then the previous session information at the client and server is cleared. If cleansession=false, the previous session is resumed. If no previous session exists, a new session is started.

This is a boolean value that controls how many messages can be in-flight simultaneously. Setting reliable to true means that a published message must be completed (acknowledgements received) before another can be sent. Attempts to publish additional messages receive an MQTTCLIENT_MAX_MESSAGES_INFLIGHT return code. Setting this flag to false allows up to 10 messages to be in-flight. This can increase overall throughput in some circumstances.

An optional array of null-terminated strings specifying the servers to which the client will connect. Each string takes the form protocol://host:port. protocol must be tcp or ssl. For host, you can specify either an IP address or a host name. For instance, to connect to a server running on the local machines with the default MQTT port, specify tcp://localhost:1883. If this list is empty (the default), the server URI specified on MQTTClient_create() is used.

Sets the version of MQTT to be used on the connect. MQTTVERSION_DEFAULT (0) = default: start with 3.1.1, and if that fails, fall back to 3.1 MQTTVERSION_3_1 (3) = only try version 3.1 MQTTVERSION_3_1_1 (4) = only try version 3.1.1